1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device having a resin-encapsulation type power semiconductor element.
2. Description of the Background Art
Power semiconductor devices such as an IGBT (Insulated Gate Bipolar Transistor), a diode, a GTO (Gate Turn-Off Thyristor), and a transistor are used under a high voltage of more than several hundreds volts. Therefore, it is necessary to maintain the insulation performance within these semiconductor devices. Thus, most of the semiconductor devices are configured such that each semiconductor element is sealed with an insulating resin.
Furthermore, since the above-described semiconductor device generally generates considerable heat, it is often equipped with a heat dissipation device such as a heat dissipation fin and a heat sink for cooling the element generating heat.
For example, Japanese Patent Laying-Open No. 2002-110867 discloses a semiconductor device in which a semiconductor element covered by a mold resin sealing body is heated and pressure-bonded onto the insulating layer printed on the surface on which a heat dissipation fin is mounted. The semiconductor element in this semiconductor device is configured such that the end of the insulating layer in plan view is located outwardly of the end of the lead frame in plan view, that is, the insulating layer is greater than the lead frame in plan view. Consequently, the insulation performance of the insulating layer is maintained.
Furthermore, for example, Japanese Patent Laying-Open No. 2005-235992 discloses a semiconductor device having a configuration in which a semiconductor module is attached to a heat sink with a screw. In the semiconductor device disclosed in this document, for the purpose of fixing the semiconductor module on the heat sink, a rebound leaf spring and a reinforcing beam are disposed on the semiconductor module, through which a screw is passed for fixation of these components. The rebound leaf spring has a slit formed therein to enhance the flexibility by which the rebound leaf spring is deformed in the direction in which the screw is tightened. This allows suppression of stress concentration resulting from the tightening force of the screw, unevenness of the tightening force, and damage to the rebound leaf spring.
For example, as disclosed in Japanese Patent Laying-Open No. 2002-110867, the semiconductor element that is conventionally used is generally fixed with a screw onto the heat dissipation plate adhered onto the heat dissipation fin using silicone grease. Silicone grease is applied in order to stably fix the heat dissipation plate onto the heat dissipation fin. However, silicone grease is inferior in thermal conductivity, for example, as compared with metal material. For this reason, use of silicone grease may cause deterioration of the thermal conductivity between the heat dissipation plate and the heat dissipation fin. Consequently, the heat dissipation performance of the semiconductor element disposed on the silicone grease may deteriorate.
Furthermore, in the semiconductor device disclosed in Japanese Patent Laying-Open No. 2005-235992, the heat dissipation performance is improved by improving the tightening state in the case where a semiconductor module and a heat sink are fixed using a screw. However, the above-mentioned document fails to disclose the improvement of the insulation performance between the semiconductor module and the heat sink.
Furthermore, Japanese Patent Laying-Open No. 2005-235992 discloses the state of the bottom of the semiconductor module but fails to disclose the state within the semiconductor module. If the module including a semiconductor element is entirely covered with resin, this resin may decrease the efficiency of dissipating the heat of the semiconductor element.
The present invention has been made in light of the above-described problems. An object of the present invention is to provide a semiconductor device capable of improving the cooling performance for the semiconductor element while ensuring the insulation performance between the semiconductor element and the component attached to the outside of the semiconductor element.